1. Field of the Invention
The present invention relates to a network call control system, in particular, to a network call control system which carries out high-grade services such as number portability and so forth.
2. Description of the Related Art
As one of measures for achieving proper competition between telephone companies, there are high-grade services such as number portability. The number portability is a service which enables a subscriber to use a telephone number particular to the subscriber wherever the subscriber is registered in a network, and enables the subscriber to move.
In the related art, in order to realize the above-mentioned high-grade services, there is a method of using an advance intelligent network (AIN). FIG. 1 shows an arrangement of one example of the advance intelligent network which realizes the high-grade services. In the figure, exchanges A, B and C are mutually connected by call control signal lines (which will be simply referred to as signal lines hereinafter) for control channels and circuits. An SCP (Service Control Point) 10 in the advanced intelligent network is connected to the exchange A by the signal line. For connection between the exchange A and SCP 10, generally, a TCAP (Transaction Capabilities Application Part) protocol is used.
In this case, when a master subscriber Sub-a1 of the exchange A dials a subscriber directory number PN (=personal directory number), to which number the number portability is applied, the exchange A inquires of the SCP 10 through the-signal line in order to obtain an actual slave directory number NN (=network directory number) from this dial number DN. When the exchange A receives the slave directory number NN from the SCP 10, the exchange A analyzes the dial number DN again, performs route determination and capture of the circuit, and sends a call-out signal to the slave station (for example, the exchange C). FIG. 2 shows a channel capture sequence at this time.
Further, recently, there is a method in which the above-mentioned high-grade services are realized using an SN (Service Node) station, shown in FIG. 3, which is obtained as a result of functions similar to those of the SCP being added to an exchange. The exchanges A, B and C are mutually connected by the signal lines for the control channels and the circuits. Further, each of the exchanges A, B and C, and the SN station 12 are connected by the signal line and the circuit in the common-line signal system. Because the SN station also acts as an exchange node, an ISUP (ISDN User Part) which is a basic protocol for exchange nodes is used for connection between each of the exchanges A, B and C, and the SN station 12.
In this case, when the master subscriber Sub-a1 dials the subscriber number PN (=personal number), to which number the number portability is applied, the exchange A captures the circuit between the exchange A and the SN station 12, and, then, sends the call-out signal to the SN station, in order to obtain the actual slave number NN (=network number) from this dial number DN.
When the SN station 12 converts the subscriber number PN into the slave number NN, the SN station 12 sets the conversion result in a call release signal as additional information, and sends it to the exchange A. (Here, in order to release the circuit between the exchange A and the SN station 12, sending of the call release signal is needed.) When the exchange A receives the slave number NN through the call release signal from the SN station 12, the exchange A analyzes the dial number DN again, performs route determination and capture of the circuit, and sends the call-out signal to the slave station (for example, the exchange C). The channel capture sequence at this time is shown in FIG. 4.
In the case where the TCAP protocol is used in the advanced intelligent network in the related art, it is necessary to load the TCAP protocol in each exchange. Further, when the number of kinds of the high-grade services to be provided increases, functions should be added not only on the side of the SCP 10 but also on the side of each exchange. Therefore, it is difficult to provide the services timely.
Further, in the high-grade service such as the number portability, the signal traffic can be reduced when the signal is sent out from the exchange at the time at which the slave number NN is determined. However, because the TCAP is a protocol which cannot deal with lines, it is necessary that the SCP 10 is sure to return the control to the master exchange A, and the master exchange A captures the circuit between the master exchange A and the slave station.
Further, in the case where the high-grade services are realized through the SN station having the exchange function, the ISUP which is the basic protocol for exchange nodes is used for the connection between each exchange and the SN station 12. Therefore, the circuit should be captured, and the signal traffic increases.
The present invention has been devised in consideration of the above-mentioned points, and an object of the present invention is to provide a network call control system in which an increase in the number of kinds of the services to be provided can be coped with simply through addition of functions in the service station, and an increase in the signal traffic can be prevented at the time of the call-out request.
In a network call control system according to the present invention, in which system a network comprises a plurality of exchanges, each exchange of the plurality of exchanges and a service station, which carries out network services, being connected through a call control signal line, and the respective exchanges of the plurality of exchanges being connected through circuits,
each exchange of the plurality of exchanges comprises a virtual-index capture processing portion which captures a virtual circuit identification index; and
the exchange specifies the virtual circuit identification index and makes a call-out request to the service station.
In this system, because the virtual circuit identification index is specified and the call-out request is made to the service station using the call control signal line, it is not necessary to capture the circuit at the time of the-call-out request. Thereby, it is possible to prevent an increase in the signal traffic.
Each exchange of the plurality of exchanges may comprise a replacement processing portion which receives a response signal sent from an opposite station in response to the call-out request, and replaces the virtual circuit identification index with an actual circuit identification index.
In this arrangement, because each exchange receives the response signal sent from the opposite station in response to the call-out request, and replaces the virtual circuit identification index with the actual circuit identification index, the circuit can be determined based on the actual circuit identification index.
The service station may comprise an intra-network inter-station management portion which manages the circuit identification indexes between the respective exchanges of the plurality of exchanges; and
the service station receives the call-out request and captures the actual circuit identification index.
In this arrangement, because the service station manages the circuit identification indexes between the respective exchanges of the plurality of exchanges, receives the call-out request and captures the actual circuit identification index, it is possible to determine the slave exchange when the call-out request occurs from the master exchange, and to determine the circuit.
The service station may comprise an intra-network calling condition management portion which manages a calling condition for each dial number.
In this arrangement, because the service station manages the calling condition for each dial number, it is possible to determine whether or not connection to the slave subscriber is possible, to perform xe2x80x98busyxe2x80x99 processing when the connection is not possible so as to prevent resources in the network from being uselessly captured, and to reduce the load on the exchange.
Each exchange of the plurality of exchanges may comprise a service-information setting processing portion which adds service identification information to the virtual circuit identification index in accordance with a result of analysis of a dial number.
In this arrangement, because each exchange adds the service identification information to the virtual circuit identification index in accordance with the result of the analysis of the dial number, the service station can determine, from the virtual circuit identification index, the service to be carried out.
The service station may comprise a service determination processing portion which determines, from service identification information added to the virtual circuit identification index, the service to be carried out.
In this arrangement, because the service station determines, from the service identification information added to the virtual circuit identification index, the service to be carried out, it is possible to reduce the processing time.